Earth-boring tools having cutting elements with cutting faces exhibiting multiple coefficients of friction, and related methods

ABSTRACT

An earth-boring tool having at least one cutting element with a multi-friction cutting face provides for the steering of formation cuttings as the cuttings slide across the cutting face. The multi-friction cutting element includes a diamond table bonded to a substrate of superabrasive material. The diamond table has a cutting face formed thereon with a cutting edge extending along a periphery of the cutting face. The cutting face has a first area having an average surface finish roughness less than an average surface finish roughness of a second area of the cutting face, the two areas separated by a boundary having a proximal end proximate a tool crown and a distal end remote from the tool crown.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/660,716, filed Mar. 17, 2015, pending, which is a divisional of U.S.patent application Ser. No. 13/461,388, filed May 1, 2012, now U.S. Pat.No. 8,991,525, issued Mar. 31, 2015, the disclosure of which is herebyincorporated herein in its entirety by this reference. This applicationis also related to U.S. patent application Ser. No. 14/480,293, filedSep. 8, 2014, now U.S. Pat. No. 9,650,837, issued May 16, 2017, for“Multi-Chamfer Cutting Elements Having a Shaped Cutting Face andEarth-Boring Tools Including Such Cutting Elements,” and to U.S. patentapplication Ser. No. 13/840,195, filed Mar. 15, 2013, now U.S. Pat. No.9,428,966, issued Aug. 30, 2016, for “Cutting Elements for Earth-BoringTools, Earth-Boring Tools Including Such Cutting Elements, and RelatedMethods,” which is a utility conversion of U.S. Provisional PatentApplication Ser. No. 61/771,699, filed Mar. 1, 2013, for “CuttingElements for Earth-Boring Tools Including Such Cutting Elements, andRelated Methods.”

TECHNICAL FIELD

The present disclosure relates to cutting elements for earth-boringtools having cutting surfaces with two or more areas exhibitingdifferent frictional characteristics, and to methods of forming suchdevices.

BACKGROUND

Earth-boring tools for forming wellbores in subterranean earthformations may include a plurality of cutting elements secured to abody. For example, fixed-cutter earth-boring rotary drill bits (alsoreferred to as “drag bits”), reamers, back-up cutters, drilling-withcasing tools, reaming-with casing tools, and exit mills may include aplurality of cutting elements that are fixedly attached to a body of thetool.

The cutting elements used in such earth-boring tools often includepolycrystalline diamond compact (often referred to as “PDC”) cuttingelements, which are cutting elements that include a polycrystallinediamond (PCD) material. Such polycrystalline diamond cutting elementsare formed by sintering and bonding together relatively small diamondgrains or crystals under conditions of high temperature and highpressure in the presence of a catalyst (such as, for example, cobalt,iron, nickel, or alloys and mixtures thereof) to form a layer ofpolycrystalline diamond material on a cutting element substrate. Theseprocesses are often referred to as high temperature/high pressure (or“HTHP”) processes. The cutting element substrate may comprise a cermetmaterial (i.e., a ceramic-metal composite material) such ascobalt-cemented tungsten carbide. In such instances, the cobalt (orother catalyst material) in the cutting element substrate may be drawninto the diamond grains or crystals during sintering and serve as acatalyst material for forming a diamond table from the diamond grains orcrystals. In other methods, powdered catalyst material may be mixed withthe diamond grains or crystals prior to sintering the grains or crystalstogether in an HTHP process.

PDC cutting elements commonly have a planar, disc-shaped diamond tableon an end surface of a cylindrical cemented carbide substrate. Such aPDC cutting element may be mounted to an earth-boring rotary drag bit orother drilling or reaming tool using fixed PDC cutting elements in aposition and orientation that causes a peripheral edge of the diamondtable to scrape against and shear away the surface of the formationbeing cut as the tool is rotated within a wellbore. Other types ofcutting elements, such as carbide cutting elements or carbide-coveredPDC cutting elements are also used in subterranean drilling operations.It has been found that cutting elements having a cutting face with asurface finish roughness in the range of 0.3 microinch (0.3 μin.) to 2.0microinches (2.0 μin.) root mean square (RMS), which may be referred toas a “polished” cutting face, exhibit favorable performancecharacteristics as the cutting element shears formation material fromthe formation being cut, including, for example, the shearing offormation chips of uniform thickness that slide in a substantiallyunimpeded manner up the cutting face of the cutting element instead ofagglomerating as a mass on the cutting face, accumulating in a fluidcourse rotationally ahead of the cutting element and potentially causing“balling” of formation material on the tool face, resulting in severedegradation of drilling performance of the rotary drag bit or otherdrilling or reaming tool.

The drilling action of the tool generates cuttings of subterraneanformation material at a cutting edge of the cutting element, whichcuttings or “chips” travel on the cutting face of the cutting elementtoward the evacuation areas of the tool, such as junk slots, and fromthere to the surface transported by drilling mud.

BRIEF SUMMARY

This summary does not identify key features or essential features of theclaimed subject matter, nor does it limit the scope of the claimedsubject matter.

In some embodiments, the present disclosure includes an earth-boringtool with a tool crown and at least one cutting element attachedthereon. The cutting element comprises a superabrasive material and hasa cutting face with a cutting edge extending along a periphery of thecutting face. The cutting face comprises at least a first area and atleast a second area. The at least a first area has a first averagesurface roughness, and the at least a second area has a second averagesurface roughness which is greater than the average surface roughness ofthe at least a first area.

The first at least a first area and the at least a second area of thecutting face are located in a manner to cause the at least a second areato provide a greater sliding friction force than a greater slidingfriction force provided by the at least a first area to a chip ofsubterranean formation material as the chip moves over the cutting face.This friction differential between the at least a first area and the atleast a second area may impede movement of the chip over the at least asecond area, causing the chip to move in a desired direction over thecutting face and enable “steering” of the chip.

In yet other embodiments, the present disclosure includes a method offorming an earth-boring tool. The method includes attaching a pluralityof cutting elements to a tool crown. At least one of the cuttingelements has a cutting face provided thereon. The cutting face has atleast a first area and at least a second area, the at least a first areahaving an average surface roughness less than an average surfaceroughness of the at least a second area. The method also includesorienting a boundary between the at least a first area and the at leasta second area so that a proximal end of the boundary is adjacent to aprofile of the tool crown at the location of attachment on the toolcrown and a distal end of the boundary is remote from the tool crown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a typical earth-boring tool.

FIG. 2 illustrates a simplified perspective view of a cutting elementshowing a cutaway portion.

FIG. 3 illustrates a simplified cross-sectional view of a cuttingelement.

FIG. 4 illustrates a simplified front view of a cutting element similarto the cutting element of FIG. 3 having a polished surface and anunpolished surface.

FIG. 5 illustrates a side elevation of the cutting element as thecutting element engages and cuts a subterranean formation and aformation chip is cut and slides over the cutting face of the cuttingelement.

FIG. 6 illustrates a front elevation of the cutting element of FIG. 5showing the formation chip being urged toward a portion of the cuttingface having a higher coefficient of sliding friction.

FIG. 7 illustrates an example of a surface finish profile of anunpolished cutting face of a cutting element.

FIG. 8 illustrates an example of a surface finish profile of a polishedcutting face of a cutting element.

FIGS. 9 through 11 and 13 through 27 illustrate different orientationsof the cutting face.

FIG. 9 illustrates a front elevation view of a cutting face having asecond area with a coefficient of sliding friction greater than acoefficient of sliding friction of a first area, a boundary between thefirst and second areas is linear and coincides with the verticalcenterline of the cutting face, the first and second areas are orientedto urge a chip toward the second area and laterally away from the centerof the cutting face.

FIG. 10 illustrates a front elevation view of a cutting face having anarcuate boundary between the first and second areas of the cutting face,the first and second areas are oriented to urge the chip toward thesecond area of the cutting face and laterally away from the center ofthe cutting face.

FIG. 11 illustrates a front elevation view of a cutting face having thefirst and second areas oriented at an acute angle with respect to thevertical centerline of the cutting face, the first and second areas areoriented to urge the chip toward the second area of the cutting face andaway from the center of the cutting face.

FIG. 12 illustrates the cutting element of FIG. 9 having a wear-flatworn into the cutting element.

FIG. 13 illustrates a front elevation view of a cutting face wherein thesecond area occupies one quadrant of the cutting face.

FIG. 14 illustrates a front elevation view of a cutting face wherein thefirst and second areas each occupy two non-consecutive quadrants of thecutting face.

FIG. 15 illustrates a front elevation view of a cutting face wherein thefirst and second areas are divided into sectors of non-equivalentsurface area by a linear boundary that does not extend through thecenter of the cutting face, the boundary being oriented at an angle withrespect to the vertical centerline of the cutting face.

FIG. 16 illustrates a front elevation view of a cutting face wherein thesecond area comprises two sectors on either side of the first area, thefirst area having two opposite linear boundaries with the second area,each boundary being oriented at an angle with respect to the verticalcenterline of the cutting face.

FIG. 17 illustrates a front elevation view of a cutting face wherein thesecond area comprises two sections on either side of the first area, thefirst area having two opposite arcuate boundaries with the second area.

FIG. 18 illustrates a front elevation view of a cutting face having acontinuous first area wherein the second area occupies four portions ofthe cutting face.

FIG. 19 illustrates a front elevation view of a cutting face having agenerally linear boundary between the first and second areas thatcoincides with the vertical centerline of the cutting face, the secondarea comprising a plurality of barcode-pattern etch paths.

FIG. 20 illustrates a front elevation view of a cutting face having agenerally linear boundary between the first and second areas that doesnot coincide with the center of the cutting face, the second areacomprising a plurality of barcode-pattern etch paths.

FIGS. 21 through 27 illustrate alternative orientations of the first andsecond areas that may be achieved at least by a laser etching process.

FIG. 21 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 22 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 23 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 24 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 25 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 26 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 27 illustrates a front elevation view of a cutting face having analternative orientation of the first and second areas.

FIG. 28 illustrates a perspective view of a cutting element having oneor more marks on a rear surface of a substrate of the cutting element.

FIG. 29 illustrates a front view of an unpolished cutting element priorto being formed into a multi-friction cutting element.

FIG. 30 illustrates a front view of the cutting element of FIG. 29having an area of the cutting face polished and a second area remainingunpolished.

FIG. 31 illustrates a front view of a polished cutting element prior tobeing formed into a multi-friction cutting element.

FIG. 32 illustrates a front view of the cutting element of FIG. 31having a first area of the cutting face “roughened” and an arearemaining polished.

FIG. 33 illustrates a perspective view of a polished cutting elementblank prior to being cut.

FIG. 34 illustrates a perspective view of the polished cutting elementblank of FIG. 33 being cut and separated to form a first half of amulti-friction cutting element.

FIG. 35 illustrates a perspective view of an unpolished cutting elementblank prior to being cut.

FIG. 36 illustrates a perspective view of the unpolished cutting elementblank of FIG. 35 being cut and separated to form a second half of amulti-friction cutting element.

FIG. 37 illustrates a perspective view of a multi-friction cuttingelement formed by bonding the first and second halves depicted in FIGS.34 and 36.

FIG. 38 illustrates a perspective view of a multi-friction cuttingelement having a non-planar cutting face.

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual views ofany particular cutting element, structure, or device, but are merelyidealized representations that are used to describe embodiments of thedisclosure.

Any headings used herein should not be considered to limit the scope ofembodiments of the invention as defined by the claims below and theirlegal equivalents. Concepts described in any specific heading aregenerally applicable in other sections throughout the entirespecification.

A number of references are cited herein, the entire disclosures of whichare incorporated herein in their entirety by this reference for allpurposes. Further, none of the cited references, regardless of howcharacterized herein, is admitted as prior art relative to the inventionof the subject matter claimed herein.

The present disclosure includes earth-boring tools having cuttingelements having a cutting face with at least two portions, which mayalso be characterized as areas, the first portion of the cutting facehaving a different coefficient of sliding friction than the secondportion. The portions of the cutting face may be polished or roughenedto achieve the desired friction coefficient thereon. The cuttingelements may include a table of superabrasive material having a cuttingface and bonded to a supporting substrate along an interface oppositethe cutting face. The inventors have discovered that cutting elementsexhibiting such frictional characteristics can influence the directionof formation chip flow over the face of the cutting element, in additionto the size and character of the chip. The present disclosure alsoincludes methods of forming such cutting elements. Examples of suchcutting elements and methods of forming the cutting elements aredisclosed in further detail below.

FIG. 1 of the drawings depicts an earth-earth boring tool 10, shown asbeing a rotary drill bit, having a body 12 secured to a shank (notshown) having a threaded pin connection thereon, whereby the drill bit10 is made up to the end of a drill string or to a down hole motordisposed at the end of a drill string (not shown). Cutting elements 14are shown secured in a predetermined pattern and at predeterminedheights and orientations on the face of a bit crown 16 to provideeffective cutting for the formation type to be cut, nozzles 18 on body12 being positioned to clear chips of formation material leaving cuttingelements 14 through evacuation features of the bit 10, including fluidcourses 20 and junk slots 22. The bit body 12 may further include aplurality of blades 24 that are separated by the junk slots 22. Thecutting elements 14 may be mounted on the crown 16 of the bit body 12 incutting element pockets that are located along each of the blades 24. Itis to be appreciated that the cutting elements, as disclosed in moredetail below, may be utilized on a crown or body of any earth-boringtool, and are not limited to use on drill bits. For example, anydownhole tool, such as reamers, back-up cutters, drilling-with casingtools, reaming-with casing tools, exit mills, and stabilizer pads, asnon-limiting examples, may be fitted with cutting elements attached to acrown or body thereof wherein the cutting elements exhibit multiplecoefficients of sliding friction capable of influencing the direction offormation chip flow over the face of the cutting element. Furthermore,cutting elements exhibiting such frictional characteristics may be usedto advantage to influence the direction of chip flow of metalliccuttings, such as occurs when a downhole mill, such as a casing exitmill, is used to mill through metallic downhole components.

Referring to FIG. 2, a partially cut-away perspective view of a cuttingelement 14 is shown. Cutting element 14 includes a substrate 26 having atable 28 of superabrasive material, such as a PDC, thereon. Withcontinued reference to FIG. 2, the diamond table 28 may be formed on thesubstrate 26, or the diamond table 28 and the substrate 26 may beseparately formed and subsequently attached together. FIG. 3 is anenlarged cross-sectional view of the cutting element 14 shown in FIG. 2.As shown in FIG. 3, the diamond table 28 may have a chamfered edge 30.The chamfered edge 30 of the cutting element 14 has a single chamfersurface 32, although the chamfered edge 30 also may have additionalchamfer surfaces, and such chamfer surfaces may be oriented at chamferangles that differ from the chamfer angle of the chamfer surface 32, asknown in the art. In lieu of chamfered edge 30, the cutting face end maybe rounded, as is known to those of ordinary skill in the art. Thediamond table 28 also has a side surface 33 extending from the chamfersurface 32 to the interface between the diamond table 28 and thesubstrate 26.

The substrate 26 may have a generally cylindrical shape, as shown inFIG. 2. Referring to FIG. 3, the substrate 26 may have an at leastsubstantially planar first end surface 34, and an at least substantiallyplanar second end surface 36, and a generally cylindrical lateral sidesurface 38 extending between the first end surface 34 and the second endsurface 36.

Although the first end surface 34 shown in FIG. 3 is at leastsubstantially planar, it is well known in the art to employ non-planarinterface geometries between substrates and diamond tables attachedthereto, and additional embodiments of the present disclosure may employsuch non-planar interface geometries at the interface between thesubstrate 26 and the diamond table 28. Additionally, although substratesand their cutting elements commonly have a cylindrical shape, like thatof substrate 26, other cross-sectional shapes of substrates and cuttingelements are also known in the art, and embodiments of the presentdisclosure include cutting elements having shapes other than a generallycylindrical shape. For example, tombstone-shaped cutters andrectangular-shaped cutters, as disclosed in U.S. Pat. No. 5,881,830,issued on Mar. 16, 1999 to Cooley, the entire disclosure of which isincorporated by reference herein, in additional to elliptical-facecutters, as disclosed in United States Patent Publication No.2009/0008155, published Jan. 8, 2009 to Sherwood, the entire disclosureof which is incorporated by reference herein, may also be used inaccordance with the embodiments disclosed herein.

The substrate 26 may be formed from a material that is relatively hardand resistant to wear. For example, the substrate 26 may be formed fromand include a ceramic-metal composite material (which are often referredto as “cermet” materials). The substrate 26 may include a cementedcarbide material, such as a cemented tungsten carbide material, in whichtungsten carbide particles are cemented together in a metallic bindermaterial. The metallic binder material may include, for example, cobalt,nickel, iron, or alloys and mixtures thereof. Alternatively, othersubstrate materials may be used.

With continued reference to FIG. 3, the diamond table 28 may be disposedon or over the first end surface 34 of the cutting element substrate 26.The diamond table 28 may comprise a multi-layer diamond table 28, withvarious layers of differing average diamond grain size. Diamond table 28may also comprise multiple diamond grain sizes, such as between twograin sizes and five grain sizes, by way of non-limiting example.Diamond table 28 may also comprise a multiple diamond grain sizedistribution, such as a mono-modal, bi-modal, tri-modal, tetra-modal orpenta-modal grain size distribution, by way of a non-limiting example.In a multi-layer diamond table 28, each layer may comprise a number ofdifferent average diamond grain sizes. The diamond table 28 may beprimarily comprised of polycrystalline diamond material. In other words,diamond material may comprise at least about seventy percent (70%) byvolume of the diamond table 28. In additional embodiments, the diamondmaterial may comprise at least about eighty percent (80%) by volume ofthe diamond table 28, and in yet further embodiments, the diamondmaterial may comprise at least about ninety percent (90%) by volume ofthe diamond table 28. The diamond table 28 of the cutting element 14 hasa leading surface face or cutting face 40, the outermost edge of which(as the cutting element 14 is mounted to the body 12 of drill bit 10)may be defined as a cutting edge 42 by which the cutting element 14engages and cuts the formation. In conventional, unpolished PDC cuttingelements, the cutting face 40 of PDC cutting element 14 is commonlylapped to a surface finish in the range of about 20 to 40 microinches(20 μin.-40 μin.) root mean square (“RMS”) (all surface finishesreferenced herein being RMS). A surface finish roughness in the range of20 μin.-40 μin. is relatively smooth to the touch and visually planar(if the cutting face is itself flat), but includes a number of surfaceanomalies and exhibits a degree of roughness, which is readily visibleto one even under very low power magnification, such as a 10 timesjeweler's loupe.

Smoother surface finishes are also achievable for the cutting face 40and chamfer surface 32 of the cutting element 14. For example, an areaof the cutting face 40 may be polished to a mirror finish of 0.3 μin. Byway of example and not limitation, one mode currently known to theinventors for polishing the cutting face 40 of superabrasive, such asPDC, cutting elements to obtain cutting elements having a mirror-likefinish in the range of 0.3 μin.-2.0 μin. is lapping of the cutting face40 on conventional cast iron laps known in the art using progressivelysmaller diamond grit suspended in a glycol, glycerine or other suitablecarrier liquid. The lapping is conducted as a three-step processcommencing with a 70 micron grit, progressing to a 40 micron grit andthen to a grit of about 1-3 microns in size. In contrast, standardlapping techniques for a conventional, unpolished PDC cutting elementhaving a surface finish roughness on the order of 20 μin.-40 μin. mayinclude an initial electrodischarge grinding of the cutting face and afinish lap in one step with 70 micron grit. By way of comparison of gritsize, 70 micron grit is of the consistency of fine sand or crystallinematerial, while 1-3 micron grit is similar in consistency to powderedsugar.

However, it has also been established that the normal 20 μin.-40 μin.surface roughness, averaging 30 μin., of state-of-the-art PDC cuttingelements may be smoothed to a finish of 0.3 μin. in a one-step process.The cutting elements 14, as received from the manufacturer, are placedwith their cutting faces 40 against a dry, rotating diamond wheel, asdisclosed in U.S. Pat. No. 6,145,608 to Lund et al., which disclosure isincorporated by reference in its entirety herein. It may be preferredthat the finish of at least a portion of the cutting faces 40 besmoothed to a 0.3 μin. or less surface finish roughness approaching atrue “mirror” finish. The same methodology for polishing cutting facesmay be applied to polish a chamfer 32 at the cutting edge 42 of thecutting face 40, as well as the side of the superhard table to the rearof the chamfer. To polish such surfaces, the cutting elements, held bytheir substrates, are disposed at the desired angle to the rotatingwheel. The cutting elements are themselves rotated about their axis ofsymmetry to smooth and polish the desired chamfer and side areas of thesuperhard table. Other methods of polishing the cutting face 40 may alsobe used, including the use of belt polishers.

As shown in FIG. 4, a cutting element 14 may be formed having a cuttingface 40 with a first area 44 possessing a coefficient of slidingfriction, μ₁, less than a coefficient of sliding friction, μ₂, possessedby a second area 46 of the cutting face 40. The relative differencebetween μ₁ and μ₂ causes the portion of the formation chip sliding overthe second area 46 to encounter a greater friction force, F_(f2), thanthe friction force, F_(f1), encountered by the portion of the chipsliding over the first area 44. The relationship between the frictionforce exerted on the chip and the coefficient of friction of the cuttingface 40 may be expressed in the following equation:

F _(f) =μF _(n),

where F_(f) is the friction force exerted on the chip, μ is thecoefficient of sliding friction of the surface of the cutting face, andF_(n) is the normal force exerted on the cutting face 40 by the chip.FIG. 5 depicts a cutting element 14 engaging and cutting a subterraneanformation 48. As illustrated, the cutting edge 42 of the cutting element14 is substantially fully engaged with the pristine or previously uncutand undisturbed area 50 of subterranean formation 48. Failure of theformation material occurs immediately adjacent, and forward of, thecutting edge 42. Thus, the cutting edge 42 is able to cut or shear aformation chip 52 from the formation 48 in a substantially unimpededmanner. As shown, the formation chip 52, of substantially uniformthickness, moves relatively freely from the point of contact or line ofcontact with the subterranean formation 48 from the cutting edge 42upwardly along the cutting face 40. As the cutting edge 42 engages theformation 48, a pressure differential is created between an outer orleading side 54 of the chip 52 (the side away from the cutting face 40)and an inner side 56 of the chip 52 immediately abutting the cuttingface 40. This pressure differential, in addition to the reactive forceof the formation 48 (and the chip 52) pressing back against the cuttingface 40, results in the normal force, F_(n), of the chip 52 against thecutting face 40. Thus, referring to FIGS. 4 and 5, the relationshipbetween the coefficient of sliding friction of the first area 44 and thesecond area 46 and the friction force exerted on the chip by the firstarea 44 and the second area 46 may be expressed, respectively, by thefollowing equations:

F _(f1)=μ₁ F _(n), and

F _(f2)=μ₂ F _(n),

where F_(f1) is the friction force exerted on the portion of the chipsliding over the first area 44 of the cutting face 40, F_(f2) is thefriction force exerted on the portion of the chip sliding over thesecond area 46 of the cutting face 40, μ₁ is the coefficient of slidingfriction of the first area 44, μ₂ is the coefficient of sliding frictionof the second area 46, and F_(n) is the normal force that the chipexerts on the cutting face 40. The force, F_(f1), encountered by theportion of the chip sliding over the first area 44 resists the motion ofthe chip as it slides up the cutting face, in essence “braking” movementof the portion of the chip sliding over the first area 44. However, theforce, F_(f2), encountered by the portion of the chip sliding over thesecond area 46 resists the movement of that portion of the chip to agreater extent than the first area 44 resists the movement of theportion sliding over the first area 44, in essence “braking” harder onthe portion of the chip sliding over the second area 46. Thisdifferential in the friction forces, F_(f1) and F_(f2), exerted on thedifferent portions of the chip 52 results in a bending moment exerted onthe chip, effectively pulling the leading end and body of the chip 52 inthe direction of the second area 46 as it slides up the cutting face 40.Thus, the chip 52 is urged or steered toward the second area 46 and awayfrom the center of the cutting face 40, as illustrated in FIG. 6. Inthis manner, the chip 52 flow may be steered in a predetermineddirection by the relative locations of the first area 44 and the secondarea 46 on the cutting face 40 of the cutting element 14. Accordingly,the chip 52 flow may be directed favorably into the path of drillingfluid exiting the nozzles 18 (FIG. 1), toward a specific fluid course orjunk slot, toward the outer diameter, also termed the “gage,” of thetool, or in any other manner to improve the performance of the tool 10.Tests have also indicated other favorable behaviors of the chip 52 as itis sheared from the formation 48 by a multi-friction cutting element 14.For example, in addition to being urged toward the second area 46 of thecutting face 40, the chip 50 also exhibits a twisting behavior, whichmay assist in breaking the chip 52 into smaller pieces, increasing theease with which the chip 50 is urged laterally away from the center ofthe cutting face 40 and off the multi-friction cutting element 14 andfurther increasing the efficiency in which the formation cuttings aretransported by the drilling fluid up the annulus of the wellbore.

Referring again to FIG. 4, one method of providing a coefficient ofsliding friction on the first area 44 less than the coefficient ofsliding friction on the second area 46 is to provide the first area 44with a surface finish roughness less than the surface finish roughnessof the second area 46. For example, the first area 44 of the cuttingface 40 may be polished to a surface finish roughness of about 0.3 μin.,while the second area 46 may have a standard surface finish roughnessfor PDC cutting elements of about 20 μin.-40 μin. When the first area 44has a polished surface finish roughness in the range 0.3 μin.-2.0 μin.and the second area 46 has a surface finish roughness greater than thesurface finish roughness of the first area 44, the differential in therelative coefficients of friction, μ₁ and μ₂, of the first area 44 andthe second area 46 described above may be achieved. Other non-limitingexamples of the relative surface finishes of the first area 44 and thesecond area 46 are now provided. The first area 44 may be polished to asurface finish roughness of about 2.0 μin. while the second area 46 mayhave a surface finish roughness of about 20-40 μin. Alternatively, thefirst area 44 may be polished to a surface finish roughness of about 0.3μin. while the second area 46 may have a surface finish roughness ofabout 2.0 μin. The degree of difference between the surface finishroughness of first area 44 and that of second area 46 may be selected toalter the bending moment applied to a chip 52 moving over the cuttingface 40, and thus the directionality of the chip's movement.Accordingly, different surface finish combinations may be employed forcutting elements 14 at different locations on the tool face, to providepreferred steering of chips at the various locations. It is to beappreciated that providing the first area 44 with a coefficient ofsliding friction different than a coefficient of sliding friction of thesecond area 46, as described above, may also be utilized to advantagewith alternative types of cutting elements. For example, cutting element14 may alternatively be a carbide-covered PDC cutting element. In yetother embodiments, the cutting element 14 may have a carbide table or aceramic table, instead of a diamond table, bonded to the substrate.Additionally, yet other various types of cutting elements may utilizethe embodiments disclosed herein to advantage, and the presentdisclosure is not limited only to the types of cutting elementsexpressly described herein.

The cutting element 14 of FIG. 4 may also have a first chamfer surface58 at a periphery of the first area 44 of the cutting face 40 and asecond chamfer surface 60 at a periphery of the second area 46 of thecutting face 40. The first chamfer surface 58 may be polished to havesubstantially the same surface finish roughness as the first area 44,and the second chamfer surface 60 may be formed to have substantiallythe same surface finish roughness as the second area 46. Additionally,portions of the side surface 33 (FIG. 3) of the cutting element 14 maybe polished to any of the surface finish roughnesses described above.

It is also within the scope of the embodiments disclosed herein topolish the cutting surfaces (cutting face 40, chamfer surfaces 32, 58,60, side surface 33, etc.) by other means, such as ion beams orchemicals, although the inherently inert chemical nature of diamondmakes the latter approach somewhat difficult for diamond.

It is to be appreciated that other methods may be used to provide thediffering coefficients of friction on the first area 44 and the secondarea 46 of the cutting face 40, including providing different materialcompositions on or within the diamond table 28 including, withoutlimitation, the use of different diamond grain sizes over differentareas of the cutting face 40. It is also contemplated that surfaceroughness differences may be effected by selective deposition of adiamond film over an area of a cutting face 40, chamfer surfaces 32, 58,60, side surface 33, etc., using chemical vapor deposition (CVD)techniques including, for example, plasma-enhanced CVD (PECVD) bymasking an area or areas over which the diamond film is not to bedeposited.

Referring to FIGS. 7 and 8, the difference in surface topography betweenan area of the cutting face 40 of a polished cutting element 14 having asurface finish roughness in the range of about 0.3 μin.-2.0 μin. andthat of an area of the cutting face 40 of a cutting element 14 having asurface finish roughness in the range of about 20 μin.-40 μin. will bereadily appreciated. FIGS. 7 and 8 comprise renderings as if portions ofa diamond or other superabrasive table were sectioned perpendicular tothe cutting face, and not tracings of actual photomicrographs. In FIG.7, an area of a cutting face 40 of a diamond table 28 having a surfacefinish roughness in the range of about 20 μin.-40 μin. is shown tocontain microscopic “peaks” 62 and “valleys” 64 in the surface 66. Suchminute elements may always be present, as well as large “ranges” or“waves” 68 and “canyons” or “troughs” 70, which comprise the majortopographic features or perturbations on cutting face 40. It is theseranges or waves 68 and canyons or troughs 70 and not the much smallermicroscopic peaks 62 and valleys 64 in surface 66 which provide orresult in the 20 μin.-40 μin. surface roughness of the cutting face 40.FIG. 8, on the other hand, depicts how such waves or ranges 68 are ofmarkedly reduced height and canyons or troughs 70 of markedly reduceddepth in a cutting face area having a surface roughness in the range of0.3 μin.-2.0 μin. Broken lines 72 provide a reference baseline withineach area of diamond table 28 from which to view the relative surfaceroughness of the cutting face areas of cutting element 14. Thus, inmicroscopic terms, the surface smoothing, which takes place in producinga cutting element with a mirror surface finish area effects amodification and reduction of relatively large-scale features of thesurface topography, and not an elimination of individual inclusions inand protrusions from the surface itself. Of course, some significantreduction in potential nucleation sites or flaw sites is achieved, aspreviously noted. Furthermore, one could smooth and polish a curved,ridged, waved, or other cutting nonlinear face area in accordance withthe methods discussed above to remove and reduce both large and smallasperities, resulting in a mirror finish cutting face area, whichnonetheless is not flat in the absolute sense.

Tests have indicated that, in addition to relative reduction in normaland tangential loading experienced using polished cutting faces versuslapped cutting faces, there is also a marked difference in theappearance of the formation chips and kerf (trough left by the cuttingelement). Chips cut by the polished cutting face PDC cutting elementwere of substantially uniform thickness and substantially continuousappearance. The kerf cut by the polished cutting element was verysmooth, almost machined in uniformity, while the kerf cut by thestandard lapped cutting element possessed an irregular profile andbottom surface.

To quantify the results achievable by a polished cutting face 40, when aPDC cutting element is polished to 0.3 μin. mirror surface finishroughness, calculations based upon force data show the coefficient ofsliding friction to be reduced to about half, or fifty percent, of thatof a 20 μin.-40 μin. standard finished, but otherwise identical, PDCcutting element. Thus, it can be said that reducing sliding contactstresses between the cutting face and formation chip can be definedmacroscopically as achieving a low friction PDC, diamond or othersuperhard material table. Such a reduction in coefficient of slidingfriction may be employed, beneficially, in embodiments of the presentdisclosure to effect preferential formation chip steering, as describedabove. Furthermore, cutting elements 14 exhibiting multiple frictionalcharacteristics, as described above, may advantageously affect the powerrequirements related to operating a downhole tool fitted with suchcutting elements 14.

While the present embodiments have been described with reference toindividual cutting elements mounted at separate locations on a toolface, it is contemplated that the present embodiments have equal utilitywith blade-type tools wherein very large, substantially continuouscutting faces are presented to engage the formation. Such cutting facesmay be fabricated from adjacent round, square or otherwise shapedindividual cutting elements of the same or different material, closelyspaced and with cooperative or even interlocking borders. The individualcutting elements may have different cutting face roughnesses, and beassembled into a larger mosaic cutting face having areas of differentcoefficients of friction. Convex, concave or other arcuately surfacedcutting elements may be polished, as may the alternate geometry(stepped, ridged, waved, etc.) cutting element surfaces.

FIGS. 9 through 12 are front elevation views illustrating examples ofdifferent orientations of the first area 44 and the second area 46 ofthe cutting face to urge the formation chip 52 in predetermineddirections (indicated by the arrow) as it slides up the cutting face ofthe cutting element 14.

FIG. 9 is a front elevation view of the cutting element 14 engaging asubterranean formation 48. In this example orientation, the first area44 and the second area 46 have a linear boundary 74 coincident with thecenter of the cutting face and substantially perpendicular to the toolcrown 16 (not shown) at the point of attachment of the cutting element14 to the tool crown 16. As illustrated in FIG. 6, in such anorientation, the higher friction force encountered by the portion of thechip 52 on the second area 46 in comparison to the first area 44 urgesthe chip 52 laterally away from the center of the cutting face towardthe second area 46 (as indicated by the direction of the arrow) as thechip 52 slides over the cutting face.

FIG. 10 illustrates an orientation of the first area 44 and the secondarea 46 of the cutting face having a non-linear boundary 74therebetween. As in FIG. 9, the boundary 74 between the first area 44and the second area 46 extends from a location on the cutting faceproximate a profile of the tool crown 16 at the point of attachment ofthe cutting element 14 to the tool crown 16 to an area remote from theprofile of the tool crown 16. However, as shown in FIG. 10, the boundary74 between the first area 44 and the second area 46 follows an arcuatepath from a point along the centerline of the face proximate the profileof the tool crown 16 (not shown) and arcs toward a lateral side of thecutting face remote from the profile of the tool crown 16, imparting agreater surface area to the second area 46 in relation to the first area44. However, in other embodiments, the cutting face may have an arcuateboundary 74 between the first area 44 and the second area 46 oriented ina manner to impart the second area 46 with a greater surface area thanthe first area 44.

FIG. 11 illustrates an orientation of the first area 44 and the secondarea 46 of the cutting face having a linear boundary 74 coincident withthe center of the cutting face and slanted at an acute angle θ withrespect to the centerline of the cutting face perpendicular to the toolcrown 16 (not shown) at the point of attachment of the cutting element14 to the tool crown 16. As the cutting edge 42 of the cutting element14 engages the formation 48, a formation chip 52 begins to form at thecutting edge 42. As the cutting edge 42 commences shearing the chip 52from the formation 48, a majority portion of the chip 52 in FIG. 11 isinitially in sliding contact with the first area 44 of the cutting faceand a minority portion of the chip 52 is in contact with the second area46 of the cutting face, resulting in only the minority portion of thechip 52 being “pulled” laterally by the higher friction force exerted onthe chip 52 by the second area 46 in comparison to the first area 44.However, as the chip 52 is progressively sheared from the formation 48and slides further up the surface of the cutting face, an increasinglygreater portion of the chip 52 comes into contact with the second area46 while an increasingly lesser portion of the chip 52 remains incontact with the first area 44, resulting in an increasingly greaterportion of the chip 52 being “pulled” laterally toward the second area46 by the higher friction force exerted by the second area 46 incomparison to the first area 44. The angle θ may be in the range of0°-60°. The effect of the angle θ of slant of the boundary between thefirst area 44 and the second area 46 is such that as the angle θincreases, the extent to which the chip 52 is urged laterally away fromthe center of the cutting face decreases. If the angle θ were set atmore than 60°, the steering effect would be negated and the interfacebetween the first area 44 and the second area 46 may act more as a“chip-breaker.”

As shown in FIG. 12, as the cutting element 14 progressively engages theformation, a wear-flat 76 forms at the cutting edge 42 of the cuttingelement 14. The presence of the wear-flat 76 does not eliminate theability of the cutting element 14 to steer the chip 52 laterally awayfrom the center of the cutting element 14. FIG. 12 depicts the cuttingelement 14 being oriented similarly to the cutting element illustratedin FIG. 9. In orientations wherein the boundary 74 between the firstarea 44 and the second area 46 of the cutting face is linear andcoincident with the center of the cutting face and substantiallyperpendicular to the tool crown 16 (not shown) at the point ofattachment of the cutting element 14 to the tool crown 16, the wear-flat76 formation does not affect the radius of curvature of movement of thechip 52 (indicated by the direction of the arrow) as the chip 52 isurged toward the second area 46 and laterally away from the center ofthe cutting face; however, the wear-flat 76 decreases the amount ofvertical surface area of the cutting face upon which the chip slidesacross, thus the wear-flat 76 affects the surface area of the portion ofthe cutting face from which the chip 52 exits as it slides off thecutting face. As the size of the wear-flat 76 increases, the lateralextend to which the chip 52 is urged from the center of the cutting facedecreases. It is to be appreciated that the arrows indicating thedirection of chip flow off of the cutting face are representative onlyand are not meant to depict the exact direction of chip flow.

FIG. 13 illustrates an orientation of the first area 44 and the secondarea 46 wherein the second area 46 occupies one quadrant of the cuttingface and the first area 44 occupies the remaining area of the cuttingface. FIG. 13 depicts a boundary line 74 being aligned with the verticalcenterline of the cutting face, although in other embodiments thequadrant may be aligned at an angle with respect to the verticalcenterline of the cutting face.

FIG. 14 illustrates an orientation of the first area 44 and the secondarea 46 wherein each of the first area 44 and the second area 46 occupytwo non-consecutive quadrants of the cutting face. One or more boundarylines 74 are depicted as being aligned with the vertical centerline ofthe cutting face, however, in other embodiments the quadrants may bealigned at an angle with respect to the vertical centerline of thecutting face.

FIG. 15 illustrates an orientation of the first area 44 and the secondarea 46 having a linear boundary 74 therebetween, the linear boundary 74extending from an edge of the cutting face at a point coincident withthe vertical centerline of the cutting face to an edge of the cuttingface at an angle θ with respect to the vertical centerline of thecutting face. The angle θ may be in the range of about 0°-60°.Alternatively, the linear boundary 74 at an edge of the cutting faceneed not be coincident with the vertical centerline of the cutting face.

FIG. 16 illustrates a cutting element 14, similar to the cutting elementof FIG. 15, wherein the second area 46 occupies two separate portions onopposite sides of the first area 44, there being two linear boundaries74 therebetween. Each linear boundary 74 extends from a substantiallyopposite edge of the cutting face at a point coincident with thevertical centerline of the cutting face, and extends at an angle, θ₁ andθ₂, respectively, with respect to the vertical centerline. The angles θ₁and θ₂ may each be in the range of about 0°-60°. FIG. 16 depicts thelinear boundaries 74 being parallel, although, in additionalembodiments, the linear boundaries 74 may be non-parallel. Furthermore,in other embodiments, one or both of the linear boundaries 74 need notbe coincident with the vertical centerline of the cutting face.

FIG. 17 illustrates a cutting element, similar to the cutting element ofFIG. 10, wherein the second area 46 occupies two separate, symmetricalportions on opposite sides of the first area 44, there being two arcuateboundaries 74 therebetween. In other embodiments, the two portions ofthe second area 46 are not required to be symmetrical.

FIG. 18 illustrates an additional orientation of the first area 44 andthe second area 46 in a partially ringed, quadrant pattern.

FIG. 19 illustrates an orientation of the first area 44 and the secondarea of the cutting face similar to FIG. 9, wherein the second area 46comprises a multiplicity of barcode-pattern etch paths 75. The etchpaths 75 may be formed using a laser etching process to “roughen”portions of a polished cutting face, as will be disclosed in more detailbelow. One or more lasers may be positioned and controlled in a manneranalogous to standardized computer numerical control (CNC) machiningprocesses. The one or more lasers may be configured to emit a beam ofelectromagnetic radiation at any wavelength that will be at leastpartially absorbed by the cutting face of the diamond table in a mannerto roughen the second area 46 of the cutting face along the etch paths75. Additionally, one or more gas jets may be provided to enhance theroughening of the second area 46 of the cutting face 40 by the one ormore lasers. The laser etching process is more fully disclosed in U.S.patent application Ser. No. 12/265,462, which published as U.S. PatentPublication No. 2009/0114628, which application is incorporated byreference herein in its entirety.

FIG. 20 illustrates an orientation of the first area 44 and the secondarea 46 similar to FIG. 15, wherein the second area 46 comprises amultiplicity of barcode-pattern etch paths 74. The etch paths depictedin FIG. 20 may be formed by the laser etching process discussedpreviously.

It is to be appreciated that, while FIGS. 9 through 20 illustratevarious orientations of the first area 44 and the second area 46 on thecutting face, other orientations are within the scope of the embodimentsdisclosed herein.

FIGS. 21 through 27 illustrate various alternative orientations withinthe scope of the present disclosure. It is to be appreciated that theshapes and/or orientations of the first area 44 and second area 46 maybe reflectively symmetric or reflectively asymmetric about at least twoplanes defined by x, y, and z axes of a Cartesian coordinate systemdefined to align a z axis of the coordinate system with a central axisof the cutting element 14 and to locate the center of the coordinatesystem the center of the cutting face 40. Referring to FIG. 27, thesecond area 46 may include a symmetrical pattern of spaced-apartcircular regions. The circular regions are one example of shapes thatmay be used in such an orientation, while other shapes may also be used.

FIG. 28 illustrates a perspective view of a multi-friction cuttingelement 14 having a substrate 26 bonded to a diamond table 28, thediamond table having a cutting edge 42. The second end surface 36 of thesubstrate 26 is shown having one or more marks 77 formed on thesubstrate 26 proximate the second end surface 36 in a manner to aid theprocess of orienting the cutting element when attaching the cuttingelement 14 to the tool crown. The marks 77 may be painted, etched, orotherwise formed on the substrate 26.

FIGS. 29 through 37 illustrate examples of methods that may be used toform an earth-boring tool having a plurality of cutting elementsattached to the tool crown, wherein at least one of the cutting elementsis a multi-friction cutting element.

FIGS. 29 through 32 illustrate examples of forming a multi-frictioncutting element 14 from a single existing cutting element.

The multi-friction cutting face 40, as described above, may be formed bypolishing a portion of an unpolished cutting element. FIG. 29illustrates a front view of a cutting element 78, similar to the cuttingelement 14 of FIGS. 2 and 3, and may be formed as previously describedherein. The cutting element 78 may have an unpolished cutting face 80,which may or may not have been previously lapped. A portion of thecutting face 80 on one side of a boundary line 82 may be polished toform a first area 44 with one substantially constant surface finishroughness that is less rough than the remaining unpolished area, whichforms the second area 46 and having another substantially constantsurface finish roughness different from the surface finish roughness ofthe first area 44, as shown in FIG. 30. The first area 44 may bepolished to a surface finish roughness, for example, in the range ofabout 0.1 μin.-2.0 μin. while the second area 46 may have a surfacefinish roughness in the range of about 10 μin.-400 μin. In yet otherembodiments, the entire cutting face 80 may be polished to a surfacefinish roughness less than 20 μin. prior to forming the first area 44,and the first area 44 may subsequently be formed by polishing a portionof the cutting face 80 on one side of the boundary line 82 to a surfacefinish roughness less than that of the remaining portion of the cuttingface 80 that forms the second area 46. It is to be appreciated that theboundary line 82 depicted in FIG. 29 is not required to be a centerlineof the cutting face 80. Moreover, the boundary line 82 is not requiredto be straight, although a straight boundary line 82 causes lessdifficulty in forming the first area 44 and the second area 46 of thecutting face.

Referring now to FIG. 31, the multi-friction cutting element 14 may alsobe formed by roughening a portion of a polished cutting face. FIG. 31shows a front view of a cutting element 84, similar to the cuttingelement 14 of FIGS. 2 and 3, and which may be formed as previouslydescribed herein. The cutting element 84 may have a lapped or polishedcutting face 86. The cutting face 86 may be polished to a substantiallyconstant surface finish roughness in the range of 0.3 μin.-2.0 μin, ormay be of a conventional lapped surface finish roughness in the range ofabout 20 μin.-40 μin. Subsequently, a portion of the cutting face 86 onone side of a boundary line 82 may be roughened to form the second area46 possessing a substantially constant surface finish roughness greaterthan that of the remaining polished area, which forms the first area 44,as shown in FIG. 32. The second area 46 may be roughened by a laseretching process, as disclosed previously, a chemical etching process, amechanical etching process, or an electrochemical etching process. Otherroughening processes are also within the scope of the embodimentsdisclosed herein. In additional embodiments, the first area 44 may befurther polished after the second area 46 is roughened. It is to beappreciated that the boundary line 82 depicted in FIG. 31 is notrequired to be a centerline of the cutting face 86. Moreover, theboundary line 82 is not required to be straight.

Once the multi-friction cutting element 14 is formed, it may be attachedto the crown 16 of the tool 10. As discussed above, the multi-frictioncutting element 14 may be characterized as having a plane orthogonal tothe cutting face, the cutting element 14 having a first portion on oneside of the plane and a second portion on a second, opposite side of theplane. The multi-friction cutting element 14 may be attached to the toolcrown 16 in a manner where a proximal end of the plane P is proximate toa profile of the tool crown 16 in the area where the cutting element 14is attached to the tool crown 16 and a distal end of the plane P isremote from the tool crown.

FIGS. 33 through 37 illustrate examples of methods that may be used toform a multi-friction cutting element 14 from two existing cuttingelements.

FIG. 33 illustrates a first single cutting element blank 88, similar tothe cutting element 84 of FIG. 31, having a cutting face 86 that hasbeen polished to a substantially constant surface finish roughness. Thefirst blank 88 may have a generally cylindrical shape, although othershapes may be used. The first blank 88 includes a diamond table 28bonded to a substrate 26. The diamond table 28 possesses the cuttingface 86, the outermost edge of which forms the cutting edge 42 by whichthe first blank 88 may engage and cut the formation. The diamond table28 may have a chamfered edge (not shown) including one or more chamfersurfaces (not shown). The diamond table 28 also has a side surface 33extending from the cutting edge 42 to the interface between the diamondtable 28 and the substrate 26. FIG. 33 also shows a boundary line 82imposed on the first blank 88 at a location where the first cuttingelement blank 88 is to be cut. The boundary line 82 may be aligned toproduce a symmetrical halving cut of the first blank 88, although otheralignments are within the scope of the embodiments disclosed herein.

The first blank 88 may be cut along boundary line 82, separating a firsthalf 90 of the multi-friction cutting element 14 (as shown in FIG. 34)from a first remaining portion 91 of the first cutting element blank 88.The first half 90 may be characterized as a first cutting unit.Referring now to FIG. 34, the first half 90 may be semi-cylindrical inshape, although other shapes are also within the scope of theembodiments disclosed herein. The cutting process forms a first bondingsurface 92 on the first half 90 extending the expanse of the cut. Thefirst bonding surface 92 may be substantially planar; although anon-planar first bonding surface 92 is also within the scope of theembodiments disclosed herein. The first half 90 of the multi-frictioncutting element 14 formed by the cutting process includes a firstcutting element substrate 94 bonded to a first diamond table 96 thereon.The first diamond table 96 possesses a first cutting face 98, theoutermost arcuate edge of which may be defined as a first cutting edge100. The first diamond table 96 also has a first side surface 102extending from the first cutting edge 100 to the interface between thefirst diamond table 96 and the first substrate 94. The first substrate94 may have a first forward end surface 104, and an at leastsubstantially planar first rear end surface 106, and a generallysemi-cylindrical first lateral side surface 108 extending between thefirst forward end surface 104 and the first rear end surface 106.

FIG. 35 illustrates a second single cutting element blank 88′, similarto the cutting element 78 of FIG. 29, having a cutting face 80 with asubstantially constant surface finish roughness greater than the surfacefinish roughness of the cutting face 86 of the first single cuttingelement blank 88 (FIG. 33). The second blank 88′ may have a generallycylindrical shape, although other shapes may be incorporated. Referringagain to FIG. 35, the second blank 88′ includes a diamond table 28′bonded to a substrate 26′. The diamond table 28′ possesses the cuttingface 80, the outermost edge of which forms a cutting edge 42′ by whichthe second blank 88′ may engage and cut the formation. The diamond table28′ may have a chamfered edge (not shown) including one or more chamfersurfaces (not shown). The diamond table 28′ also has a side surface 33′extending from the cutting edge 42′ to the interface between the diamondtable 28′ and the substrate 26′. FIG. 35 also shows a boundary line 82′imposed on the second blank 88′ at a location where the second blank 88′is to be cut. The boundary line 82′ may be aligned to produce asymmetrical halving cut of the second blank 88′, although otheralignments are contemplated to be within the scope of the embodimentsdisclosed herein.

The second blank 88′ may be cut along boundary line 82′, separating thesecond half 90′ of the multi-friction cutting element 14 (as shown inFIG. 36) from a remaining second portion 91′ of the second cuttingelement blank 88′. The second half 90′ may be characterized as a secondcutting unit. Referring now to FIG. 36, with continued reference to FIG.34, the second half 90′ may be semi-cylindrical in shape, although othershapes are also within the scope of the embodiments disclosed herein.Furthermore, the second half 90′ may be symmetrical to the first half90, although symmetry between the first half 90 and the second half 90′is not required. The cutting process forms a second bonding surface 92′on the second half 90′ extending the expanse of the cut. The secondbonding surface 92′ corresponds to the first bonding surface 92 and isconfigured to be bonded to the first bonding surface 92. The secondbonding surface 92′ may be substantially planar; although a non-planarsecond bonding surface 92′ is within the scope of the embodimentsdisclosed herein. The second half 90′ of the multi-friction cuttingelement 14 formed by the cutting process includes a second cuttingelement substrate 94′ bonded to a second diamond table 96′ thereon. Thesecond diamond table 96′ may comprise a multi-layer diamond table 96′while the first diamond table 96 may comprise a single-layer diamondtable 96, and vice versa. Furthermore, the second diamond table 96′ maycomprise a different volume percentage of diamond material than thevolume percentage of diamond material of the first diamond table 96.

The second diamond table 96′ possesses a second cutting face 98′, theoutermost arcuate edge of which may be defined as a second cutting edge100′. The second diamond table 96′ also has a second side surface 102′extending from the second cutting edge 100′ to the interface between thesecond diamond table 96′ and the second substrate 94′. It is to beappreciated that the first half 90 of the cutting element 14 may have aninterface geometry between the first diamond table 96 and the firstsubstrate 94 different than the interface geometry between the seconddiamond table 96′ and the second substrate 94′ of the second half 90′ ofthe cutting element 14. The second substrate 94′ may have a secondforward end surface 104′, and an at least substantially planar secondrear end surface 106′, and a generally semi-cylindrical second lateralside surface 108′ extending between the second forward end surface 104′and the second rear end surface 106′.

After the first half 90 is separated from the first cutting elementblank 88 and the second half 90′ is separated from the second cuttingelement blank 88′, the first bonding surface 92 of the first half 90 andthe second bonding surface 92′ of the second half 90′ may be bondedtogether to form the multi-friction cutting element 14 depicted in FIG.37. The bonding may be performed by welding or brazing. In embodimentswhere the first half 90 and the second half 90′ are bonded by a brazingmethod, a brazing alloy, such as a high-silver-content alloy, may beplaced between the first bonding surface 92 and the second bondingsurface 92′ and heated to a temperature of about 1200° F. Additionally,a flux may be used to protect the brazing alloy from oxidation duringthe brazing process. Alternatively, the first half 90 and the secondhalf 90′ may be bonded by an epoxy glue. In additional embodiments, thefirst half 90 and the second half 90′ may be mechanically coupledtogether, for example, by the use of one or more clamps, locking blocks,bolts, or other mechanical fasteners. Referring now to FIG. 37, afterthe first half 90 and the second half 90′ are bonded together, the firstcutting face 98 forms the first area 44 of the cutting face 40, and thesecond cutting face 98′ forms the second area 46 of the cutting face 40.The first area 44 and the second area 46 of the cutting face 40 maypossess any of the relative surface finish roughnesses described above.Furthermore, after the first half 90 and the second half 90′ areseparated from the first and second cutting element blanks 88, 88′,respectively, either or both of the first cutting face 98 and the secondcutting face 98′ may be further polished or roughened to form thedesirable relative surface finishes of the first area 44 and the secondarea 46. These additional finishing processes may be performed before orafter the first half 90 is bonded to the second half 90′.

In other embodiments, both the first blank 88 and the second blank 88′may have an unpolished cutting face. In such embodiments, after cuttingthe first blank 88 to form the first half 90 and cutting the secondblank 88′ to form the second half 90′, the first cutting face 98 may bepolished to the final desired surface finish roughness of the first area44 before or after bonding the first half 90 to the second half 90′.

In yet additional embodiments, both the first blank 88 and the secondblank 88′ may have a polished cutting face. In such embodiments, afterthe cutting the first blank 88 to form the first half 90 and cutting thesecond blank 88′ to form the second half 90′, the second cutting face98′ may be roughened to the final desired surface finish roughness ofthe second area 46 before or after bonding the first half 90 to thesecond half 90′.

In still further additional embodiments, the first half 90 may bepolished after the first blank 88 is cut and either before or after thefirst half 90 is bonded to the second half 90′, while the second half90′ may be roughened after the second blank 88′ is cut and either beforeor after the second half 90′ is bonded to the first half 90.

Additionally, the first remaining portion 91 of the first blank 88 andthe second remaining portion 91′ of the second blank 88′ may be bondedtogether using any of the methods described above, and optionally mayhave their respective cutting faces further processed using any of themethods described above, to form a second multi-friction cutting elementfrom the first blank 88 and the second blank 88′.

It is to be appreciated that while the cutting element 14 depictedherein has a substantially planar cutting face 40, non-planar cuttingface geometries are also within the scope of the embodiments disclosedherein. For example, a cutting element 14 having one or moreindentations or grooves in the cutting face 40 of the diamond table 28(not shown) may be utilized to advantage in accordance to theembodiments disclosed herein, as shown in FIG. 38.

The embodiments disclosed herein enable the formation of amulti-friction cutting element capable of steering formation chipcuttings in a predetermined direction off of the cutting face of thecutting element. Other methods of forming the second area 46 to have agreater coefficient of sliding friction than the first area 44 areconsidered to be within the scope of the embodiments disclosed herein,such as, for example, using a belt polisher to polish a portion of anunpolished cutting element 14.

While certain illustrative embodiments have been described in connectionwith the figures, those of ordinary skill in the art will recognize andappreciate that embodiments of the invention are not limited to thoseembodiments explicitly shown and described herein. Rather, manyadditions, deletions, and modifications to the embodiments describedherein may be made without departing from the scope of embodiments ofthe invention as hereinafter claimed, including legal equivalents. Inaddition, features from one disclosed embodiment may be combined withfeatures of another disclosed embodiment while still being encompassedwithin the scope of embodiments of the invention as contemplated by theinventor.

1. A method of forming a cutting element for an earth-boring tool,comprising: forming a superabrasive cutting face on the cutting element;forming a first area of the cutting face to have a first average surfaceroughness; and forming a second area of the cutting face to have asecond average surface roughness greater than the first average surfaceroughness, the second area comprising two or more portions separated bythe first area.
 2. The method of claim 1, further comprising forming thefirst area of the cutting face to have a surface roughness of about 0.1to about 2 microinches and the second area of the cutting face to have asurface roughness of about 10 to about 400 microinches.
 3. The method ofclaim 2, further comprising etching the two or more portions of thesecond area with a laser.
 4. The method of claim 1, further comprisinglocating the two or more portions of the second area within onesemicircular half of the cutting face, and locating the first area ofthe cutting face within the other semicircular half of the cutting face.5. The method of claim 1, wherein the first area comprises two portions,and second area comprises two portions, further comprising locating eachof the two portions of the first area and each of the two portions ofthe second area to occupy non-consecutive quadrants of the cutting face.6. The method of claim 1, further comprising locating the second area tocomprise two separate portions on opposite sides of the first area. 7.The method of claim 6, further comprising forming either linear ornon-linear boundaries between the first area and the two separateportions of the second area.
 8. The method of claim 1, furthercomprising forming the second area in two opposing quadrants of thecutting face, wherein each quadrant includes a portion of the secondarea adjacent a center of the cutting face and another portion of thesecond area adjacent a periphery of the cutting face.
 9. The method ofclaim 1, further comprising forming portions of the second area tocomprise a multiplicity of barcode-pattern mutually parallel etch paths.10. The method of claim 9, further comprising orienting the portions ofthe second area perpendicular to a diameter of the cutting face andextending from the diameter to a periphery of the cutting face.
 11. Themethod of claim 9, further comprising orienting the portion of thesecond area perpendicular to a line at an acute angle with respect to adiameter of the cutting face and extending to a periphery of the cuttingface.
 12. The method of claim 1, further comprising forming the two ormore portions of the second area to comprise concentric ring portions onthe cutting face.
 13. The method of claim 12, further comprising formingthe two or more portions of the second area to comprise segmented ringportions.
 14. The method of claim 1, further comprising forming the twoor more portions of the second area in a chevron pattern.
 15. The methodof claim 14, further comprising forming the chevron pattern to compriselinear segments.
 16. The method of claim 1, further comprising formingthe two or more portions of the second are to comprise mutually parallellinear segments, each segment extending from a diameter of the cuttingface at an oblique angle thereto to a periphery of the cutting face. 17.The method of claim 1, further comprising locating the two or moreportions of the second area as a plurality of segments locatedconcentrically about a center of the cutting face and spaced inwardlyfrom a periphery thereof.
 18. The method of claim 17, further comprisingforming at least some segments of the plurality in a polygonal shape.19. The method of claim 17, further comprising forming at least somesegments of the plurality in an elliptical shape.
 20. The method ofclaim 19, wherein forming at least some segments of the plurality in anelliptical shape comprises forming the at least some segments of theplurality in a circular shape.